Some electronic devices or systems, such as cell phones, laptops, camera recorders and other mobile battery operated devices, may include low drop-out (LDO) voltage regulators to provide relatively precise and stable direct current (DC) voltage.
FIG. 1A shows a conventional dual input power management system. As shown in FIG. 1A, two input terminals IN1 and IN2 connect to a LDO voltage regulator via a respective diode. The LDO voltage regulator selects the greater input voltage from the input terminals IN1 and IN2, and provides an output voltage VOUT on the output terminal OUT to a micro-processor (MCU). However, this does not allow input priority setting and enable setting.
Another conventional scheme is to utilize one LDO voltage regulator and multiple input power path selection switches controlled by an MCU. As shown in FIG. 1B, a power management system with dual input terminals IN1 and IN2 includes a LDO voltage regulator, an auxiliary circuit, and an MCU. The LDO voltage regulator provides an output voltage VOUT on the output terminal OUT to the MCU. The auxiliary circuit monitors whether the input terminals IN1 and/or IN2 have a power supply, and provides the power supply information to the MCU. The MCU generates enable signals EN1 and EN2 according to the power supply information, to selectively enable or disable switch 1 and switch 2 (e.g., a power switch chip). In this manner, a corresponding power supply (e.g., the power supply from the input terminal IN1 or IN2) is selected for LDO voltage regulation, thus generating the output voltage VOUT on the single output terminal OUT. However, this scheme requires that the MCU has multiple input/output interfaces (I/O) and proper firmware to control those discrete components. Thus, this is a high cost, high power consumption, high complexity solution and requires large Printed Circuit Board (PCB) space. Furthermore, since the MCU needs the auxiliary circuit to determine whether the input terminals IN1 and IN2 have a power supply, the power management system is unreliable during power mode conversion.